Murdoch is skinny, 34, and newly blond. We're chatting in Prospect Park, Brooklyn, the venue for a Belle & Sebastian gig that night. Some 8,000 locals are expected, all sweet on the (mostly) retro-pop mini-symphonies that are this Glaswegian band's forte.

Earlier the group hosted an unusual press junket at Shea Stadium in New York, doing interviews during a New York Mets vs Colorado Rockies baseball game. The novel approach to promo worked well. "It was very relaxed and there was plenty of time for a beer and a chat," he says. "Baseball's a game that comes in waves."

As Belle & Sebastian gear up for the release of their fifth album, Dear Catastrophe Waitress, all this suggests a change of tack. Until now, they have conducted media relations with caution. When 1999's The Boy with the Arab Strap scored them a Brit for best newcomer, only two of the band bothered to attend the ceremony. Their reticence, and coy, Super 8-shot videos, have at times been seen as pretentious.

Butchange is afoot. The keyboard player, Chris Geddes, concedes that signing to Rough Trade was partly contingent on playing ball with those pesky journos. "We're like any group; we want people to hear our records. We've had a really good reaction to the album, and with Trevor producing we want to give it a decent push."

Ah yes, Trevor. As in Horn. As in the erstwhile Buggles member and ongoing studio boffin best known for his slick hit-making with Frankie Goes To Hollywood, and, more recently, Tatu. How did that come about? "We played the Coachella Festival in California last year," says Murdoch. "The lady who cleaned our caravan told us she worked for Trevor, and his daughter was a fan of ours. Trevor got in touch, so we arranged a meeting out of curiosity. We all really liked him, and thought, 'Why not?'"

Anyone worried that Horn might have supplanted Belle & Sebastian's strings and reverb-drenched guitars with sequencers can relax. His sonic approach on Dear Catastrophe Waitress is very much simpatico, and this, combined with a leap forward in the band's own writing and arranging skills, has resulted in what is arguably their best album to date.

Asked what events influenced his writing, Murdoch simply says: "A break-up is always fertile ground for a songwriter." When I ask him to unpack the lyric of "Wrapped Up in Books", he laughs and says it's about "committing adultery of the mind". Surely that's harmless? "You would think so, but it can also be the beginning of the end."

It's difficult to know what to read into that remark, but a song that definitely references Murdoch's split is "I'm a Cuckoo". An ace pop number he wrote on piano, "Cuckoo" was translated into a brass and twin-lead-guitars arrangement. Any machismo has been cleverly sieved from the Thin Lizzy-esque tropes within "Cuckoo", but it's still a shock to find Belle & Sebastian tipping the hat to Phil Lynott's hedonistic rockers. What gives?

"It can't be ignored that if you're in this business you're basically trying to sustain your childhood for as long as possible," says Murdoch. "A big part of my childhood involved listening to Thin Lizzy. Phil Lynott was certainly one of my heroes. I liked those cheeky wee winks he used to do."

The Prospect Park gig is a triumph. Belle & Sebastian are infinitely better than the shambling outfit I saw back in 1999. At the end of "The Boy with the Arab Strap" there's a telling moment. Murdoch says that, as there are children in the audience, he doesn't want to sing the graphic last verse. As the crowd cheer, he lowers his eyes. It seems that part of him still wants to be The Catcher in the Rye.